Just completed a level 90 (tier four) mobile defense bounty in the zariman where the mobs have steel path modifers of health/shields/armor, but the enemy levels were appropriate for the tier selected.
Brought gear to kill a level 94 void angel and experienced the joy of felling it on steel path with no focus school buffs. Brought madurai on the next run and it played precisely like a steel path mobile defense void angel/thrax/corpus mission does. I am the host and my toggle on the star chart is set to steel path, and a client set the vote for the normal bounty, if that matters.
Edit:
After further testing, once I switched my star chart modifer to non-steel path, the issue seemed resolved. Perhaps the toggle was the culprit?